A tool for obtaining efficient, transparent, replicable measurement of social behavior would increase understanding of pathways to healthy child development. This application will validate real-time, continuous measurements of social behavior. Measurements will be made by multiple naive raters (using a joystick), whose ratings are aggregated to increase their precision and generalizability. Continuous ratings will be conducted using four already-acquired expertly coded data-sets. Ratings will include the emotional valence of high-risk infants, the joint-engagement of middle-class dyads, the symbolic play of hearing impaired children, and the negativity of families with children who have behavior problems. The application will examine the reliability of measurements made using this continuous rating software, and the convergent, concurrent, and predictive validity of these ratings. High concordance between naive raters' continuous ratings and the reliable measurements already obtained by expert coders would indicate convergent validity. Continuous ratings of behavioral qualities are also expected to differ between groups (e.g., normal vs. hearing impaired), and to change with age (i.e. 9, 18, & 24 months) and between situations (i.e., face-to-face vs. still-face) in a manner parallel to those seen in the expert coded measures. Significant associations between continuous ratings (such as time-series of infant-mother perceived emotion) made during the same assessment will indicate concurrent validity. Significant associations between continuous ratings and later outcome (such as between joint engagement and language outcome) would indicate predictive validity. Encouraging healthy development involves understanding the social behavior of typical and at-risk children interacting with their families. Current behavioral measurement systems are typically complex and time-consuming, which creates barriers to the replication of results. To maximize public health impact, a user-adjustable version of the continuous rating software will be made available for download by investigators. This will allow investigations of observers' continuous ratings of a plethora of health-relevant constructs. With this software, naive raters are provided with brief, precise descriptions of constructs, which enhances the relevance of findings to health providers and policy makers because results will reflect a scientifically defined, simple view of the construct measured. [unreadable] [unreadable] [unreadable]